In the prior art, optical elements such as electroluminescent elements for full-color display have been used for image display panels of color televisions, personal computers, cellular phones, car navigation systems and the like. Such an optical element includes a plurality of luminescent layers which are laterally disposed. One of the significant structural requirements of the optical elements is a luminescent layer having an even thickness. For example, Japanese Patent Laid-Open No. 2002-148429 and Japanese Patent Laid-Open No. 2003-272840 describe that an even thickness is obtained by specifying a contact angle of film forming ink.
FIGS. 8 and 9 are structural diagrams showing an optical element of the prior art described in Japanese Patent Laid-Open No. 2002-148429. FIG. 8 is a schematic plan view showing the optical element from above. FIG. 9 is a schematic sectional view showing the optical element along the normal of a substrate. In FIGS. 8 and 9, reference numeral 1 denotes the substrate, reference numeral 2 denotes a partition wall, reference numeral 3 denotes a pixel, and reference numeral 4 denotes a similar figure area at the center of the pixel. The similar figure area 4 is disposed at the center of the pixel 3 and has an area occupying 80% of the area of the pixel 3. Further, in FIGS. 8 and 9, reference character T denotes the maximum thickness of the partition wall 2, reference character te denotes the thickness of the outer edge of the pixel 3, reference character tmax denotes the maximum thickness of the pixel 3 in the similar figure area 4, and reference character tmin denotes the minimum thickness of the pixel 3 in the similar figure area 4.
In the prior art, the thickness te of the outer edge of the pixel 3 is at least 80% of the maximum thickness T of the partition wall 2. In the similar figure area 4 which is disposed at the center of the pixel 3 and has an area occupying 80% of the area of the pixel 3, the average thickness of the pixel 3 is less than 80% of the maximum thickness T of the partition wall 2, and a difference between the maximum thickness tmax and the average thickness and a difference between the minimum thickness tmin and the average thickness are not larger than 25% of the average thickness.
In a first manufacturing method of the optical element according to the prior art, the adhesion of ink to the partition wall 2 during the shrinkage of the ink is distinctively increased by controlling the surface roughness of the partition wall 2. In a second manufacturing method, the adhesion of ink to the partition wall 2 during the shrinkage of the ink is distinctively increased by using a photosensitive resin composition as a material of the partition wall 2 and applying the ink when the photosensitive resin composition is not cured.
Moreover, in the manufacturing methods of the optical element according to the prior art, the surface of the partition wall 2 is made ink repellent by using plasma. Thus it is possible to prevent color mixture between adjacent pixels. The degree of ink repellency on the surface of the partition wall 2 is specified such that a contact angle measured using pure water is at least 90°. Further, an affinity for ink on the surface of the substrate 1 is specified such that a contact angle measured using pure water is not larger than 20°.
However, in the technique described in Japanese Patent Laid-Open No. 2002-148429 according to the prior art, an even thickness is obtained in the similar figure area 4 by specifying the contact angle of pure water. Thus the scope of the contact angle of pure water and the scope of the contact angle of an organic solvent may be different from each other, so that a preferably even thickness may not be obtained. Further, the contact angle of pure water relative to the partition wall is set at 90° or more and the contact angle of pure water relative to the substrate is set at 20° or less. For this reason, in the technique described in Japanese Patent Laid-Open No. 2002-148429 according to the prior art, the scope of a usable contact angle is disadvantageously small.
Japanese Patent Laid-Open No. 2003-272840 describes that an even thickness is obtained by imparting repellency to the surface of a partition wall such that ink has a receding contact angle of 29° to 45° when the partition wall has an inclination angle of about 70°. In the prior art described in Japanese Patent Laid-Open No. 2003-272840, however, the inclination angle of the partition wall is disadvantageously limited to about 70°.
Further, ink generally used for manufacturing the optical element and prepared by dissolving an organic compound into an organic solvent is disadvantageously dried with complicated behaviors resulting from a plurality of combined basic dry modes, as will be described later.